1. Field of the Invention
The present invention relates to a linear guide apparatus such as a ball screw, a ball spline and a linear guide.
The present invention also relates to a ball screw and, in particular, to a ball screw which is easy to incorporate a seal thereinto and is excellent in the reliability and sealing performance of the seal.
2. Description of the Related Art
A ball screw is composed of a screw shaft and a nut screwed together with the screw shaft; and, in the outer peripheral surface of the screw shaft and in the inner peripheral surface of the nut, there are formed spiral-shaped screw grooves which are disposed opposed to each other. And, in a spiral-shaped ball rolling passage formed by and between the two screw grooves, there are disposed a large number of balls in such a manner that they are allowed to roll along the ball rolling passage, while the screw shaft and nut can be moved in the axial direction thereof with respect to each other through the rolling movements of the large number of balls.
Also, on the two end portions of the nut, there are disposed two seals which are used to seal the opening of a clearance between the screw shaft and nut. And, the two seals are respectively fixed to the nut by bolts which are inserted into axially-extending holes formed in the end face of the nut.
However, the above-mentioned conventional seal fixing method has a problem that it takes the number of man-hour to assemble the ball screw. Also, in order to secure the reliability of the seal, it is necessary to take such special measures as to be able to prevent the seals from being removed from the nut.
Conventionally, as a ball screw for use in a machine tool or the like, for example, there is also known a ball screw which is disclosed in JP-A-5-44810. A ball screw of this type includes a cylindrical-shaped nut to be fitted with the outer periphery of a screw shaft, while a spiral-shaped rolling element rolling groove is formed in the outer peripheral surface of the screw shaft. This rolling element rolling groove is disposed opposed to a rolling element rolling groove which is formed in the inner peripheral surface of the nut. In case where either the screw shaft or nut is rotated, a large number of rolling elements (balls) incorporated into the nut are allowed to roll between the above two rolling element rolling grooves.
In the thus-structured conventional ball screw, in case where a foreign substance such as cut powder gets into between the screw shaft and nut, there is a possibility that the groove surfaces of the rolling element rolling grooves and the surfaces of the rolling elements can be damaged by the foreign substance. In view of this, conventionally, annular-shaped sealing members each made of resin are mounted on the two ends of the nut and the inner periphery edge portions of the sealing members are slidingly contacted with the rolling element rolling groove of the screw shaft to thereby prevent the invasion of the foreign substance into between the screw shaft and nut.
However, in case where the above-mentioned annular-shaped sealing members are mounted on the two ends of the nut, the interior of the nut is hermetically sealed by the annular-shaped sealing members, which provides a state in which the air is sealed in the interior of the nut. In this state, even in case where a lubricant such as grease is supplied to the rolling element rolling groove of the nut from a lubricant supply hole formed in the nut, the air sealed in the interior of the nut impedes the supply of the lubricant, which makes it difficult to supply the lubricant uniformly over the entire area of the rolling element rolling groove of the nut.
Also, in case where the thickness of the annular-shaped sealing members to be mounted on the two ends of the nut is small (for example, about 0.5 mm), when the lubricant is supplied into the interior of the nut, the air sealed in the interior of the nut deforms the annular-shaped sealing members elastically to thereby fulfill the function of a valve body. This generates a pressure difference between the interior and exterior of the nut and, due to the pressure difference, there is a fear that the lubricant can leak from the surface of the rolling element rolling groove or a foreign substance can be sucked into the rolling element rolling groove surface.